The problem of colour removal from pulp and paper mill waste has been a subject of great consideration and investigation in the last few decades. An estimated two trillion gallons of wastewaters are discharged annually by the pulp and paper industry in major paper-producing countries and much of this effluent is highly coloured. (Joyce et al., 1983).
The brownish colour of the wastewater is mainly organic in nature and primarily attributable to lignin degradation products formed during various pulping and bleaching operations (Srivastava et al., 1984, Dilek et al., 2000). The other colour-imparting agents are wood-extractives, tannins, resins and synthetic dyes.
Colour was never thought to be a major problem, being classified as a non-conventional pollutant. The reasons for colour regulations at some places are said to be, protection of fisheries or aesthetic considerations. Secondly, discharge of coloured pulping effluents to the receiving waters, inhibits photosynthetic activity of aquatic biota by reducing the penetration of sunlight, besides having direct toxic effects on biota.
The colour compounds also chelate metal ions and may impart contamination by heavy metals. Recently, the colour causing organic compounds have also been implicated in the appearance of blue-green algal blooms (Paerl, 1982; Kuenzler et al., 1982; Witherspoon & Pierce, 1982). It is therefore, imperative that the colour present in pulp and paper mill effluents be removed, before being discharged into receiving waters.
There are two general strategies for the removal of colour from the effluent of a pulp & paper mill:                1) Conventional end of pipe treatment        2) Modification of the pulp and paper manufacturing process so that less colour is produced        
The following are the conventionally used colour removing technologies:                Secondary treatment: the effluents are treated with conventional activated sludge method. However, conventional biological treatment systems cannot remove colour (Yosefian et al., 2000).        Enzyme pre-treatment        Resin separation and ion exchange        Aluminium oxide        Adsorption on wood        Membrane processes        Irradiation        Electrolytic process        Activated carbon        Land treatment        Ozone        
At this point, no single colour removal technology has been identified as the most effective. Since all the above-cited technologies are cost-intensive, they would have adverse economic impact on the mill involved. Moreover, chemical treatment processes add up to the ever-increasing concentration of chemicals in the environment (Kapdam et al., 2000).
In principle, decolorization is achievable using one or a combination of the following methods;                Adsorption        Filtration        Precipitation        Chemical degradation        Photodegradation and        Biodegradation        
Rohella et al., 2001 used polyelectrolytes (commercially available) for removing colour from pulp mill effluents. However, the cost-benefit analysis of this treatment has not yet been worked upon and hence this type of technology is not viable. However, since the polyelectrolytes rely on ionic charge of the effluent, the colour reducing ability will be highly variable, considering the enormous fluctuations occurring in the composition of the wastewater.
The majority of colour removal techniques work either by concentrating the colour into a sludge or by the partial breakdown or complete breakdown of the colored molecule (Willmott et al, 1998). However, the colour and chemical composition of the pulp mill effluents are usually subject to both daily process as well as seasonal variations. A single, universally applicable end-of-pipe solution has therefore not emerged till date.
General physico-chemical colour removal methods such as chemical precipitation, rapid sand filtration, membrane processes and adsorption have been developed (Springer, 1985). Adsorption and membrane processes, although are efficient, but expensive (Manjunath and Mehrotra, 1981).
Application of electrochemical methods is another way to treat the wastewaters from the cellulose paper production (Christoskova and Lazarov, 1988). This method guarantees high treatment efficiency but its effectiveness depends upon the types of electrodes, the construction of electrocoagulators and the conditions under which the process is run.
Chemical precipitation, using alum, ferric chloride and lime has also been studied extensively (Lathia and Joyce, 1978; Dugal et al, 1976; Joyce et al, 1979; Srivastava et al, 1984; Beulker and Jekel, 1993; Stephenson & Duff, 1996). In spite of short retention times and low capital costs, there are some drawbacks reported, such as high cost of chemicals for precipitation as well as for pH adjustment, voluminous sludge production due to heavy dosages, problems associated with dewatering and disposing of generated sludge and high residual cation levels, so that their colour remains in the supernatant (Stephenson and Duff, 1996; Srivastava et al, 1984).
In theory, biological treatment gives the ideal solution to colour removal as less sludge is produced as compared to chemical treatments. Lower daily running costs are also incurred. Among the biological systems, white-rot fungi have been extensively researched upon, for their capability to degrade lignin which forms an important and major component of the pulp and paper effluents (Feijoo et al., 1995). Certain workers have shown that the pellets of white-rot fungi, under specific conditions of incubation, strongly adsorb colour and AOX from the kraft bleach plant effluent (Jaspers et al., 1996).
Raghu Kumar et al., 1996, showed that marine fungi could also be utilized for colour removal from bleached plant effluent. One of the strain was reported to give 74% decolorization at alkaline pH over a period of 14 days. Several other researchers have also reported partial decolorization by white-rot fungi (Eaton et al, 1980; Livernoche et al, 1983; Pronty, 1990; Gokcay and Dilek, 1994). Gokcay and Dilek (1994) have pointed out that due to the need for high glucose concentrations by the fungus, this treatment is economically non-feasible. They have also reported that the fungi were not effective when bleaching effluents were present.
Dilek et al., 1999 have reported the decolorization of pulping effluents using a mixed culture algae. A combination of aerobic-anaerobic treatment has been used by Vidal et al. White-rot fungi excreting several extracellular oxidative enzymes including Lignin peroxidase, Manganese peroxidase and laccases were used for decolorizing bleach kraft pulp mill effluents. Up to 64% colour was removed by applying aerobic-anaerobic treatment followed by enzyme treatment.
Till date, there are almost no reports regarding the utilization of pure bacterial cultures for decolorization of pulping effluent. The novelty of the present invention is the application of pure cultures of bacteria, isolated from natural habitat, for removing colour of the pulp and paper wastewaters in an industrially and economically viable fashion.